Recovery of lead from lead batteries is of significant economic importance, both due to the cost of obtaining lead and the problems of waste lead disposal. In standard commercial methods of recovering lead values from battery scrap, or from the active material of battery scrap, the primary treatment often involves smelting the material in a reverberatory furnace, blast furnace, or electric furnace using standard pyrometallurgical procedures. These pyrometallurgical processes have many disadvantages and drawbacks.
The main disadvantage of pyrometallurgical smelting is that the processes operate at elevated temperatures and generate substantial amounts of sulfur dioxide gas, as well as volatile dusts. The dusts can carry substantial amounts of metal, such as lead, cadmium, arsenic, antimony and the like. In addition, pollution by hydrogen chloride may result from such pyrometallurgical methods if polyvinyl chloride separators or other chloride-containing materials are present in the battery waste. Further, pyrometallurgical methods pose problems of thermal control. Moreover, such processes have become commercially less desirable due to increased fuel costs.
In order to overcome these problems, various methods for controlling emission of pollutants, or for removing potential pollutants prior to smelting have been proposed. These methods, however, do not avoid the problems of thermal control and rising fuel costs. As alternatives, various hydrometallurgical methods have been suggested. However, often such hydrometallurgical techniques do not result in recovery of metallic lead. Moreover, these methods are typically inefficient and do not effect economical recovery of substantially all lead values as metallic lead. Specifically lead peroxide is often not recovered when hydrometallurgical techniques are employed. Problems with losses of lead and with disposal of wastes containing lead are therefore presented by these methods. For these reasons, many hydrometallurgical methods have not received commercial acceptance.
The present invention provides an economical method for recovery of substantially all lead values in battery sludge as metallic lead. By means of this method, all forms of lead in battery sludge can be converted to metallic lead rapidly and efficiently. Since the process maximizes lead recovery, the problems of disposal of waste lead are minimized.
Moreover, the present process avoids the problems encountered in prior art methods for recovery of lead from battery sludge. Not only does this process substantially eliminate emission of sulfur oxides, volatile dust and chlorides but also effectively eliminates problems of thermal control, while minimizing fuel costs.
In sum, in accordance with the present invention, substantially all lead values in battery sludge may be efficiently converted to metallic lead in a manner which is enviromentally acceptable, economically competitive and suitable for large scale commercial operations.